[Tests] removing the use of GCC directives

tests/builtins/alloc.c

tests/idct/idct.c

tests/idct/ieee_1180_1990.c

tests/impact/call.i

tests/impact/first.i

tests/impact/loop.i

tests/impact/slicing.i

tests/occurrence/ptr_assert.i

tests/pdg/call.c

tests/pdg/calls_and_implicits.c

tests/pdg/calls_and_struct.c

tests/pdg/decl_dpds.c

tests/pdg/dpds_intra.c

tests/pdg/globals.c

tests/pdg/inter_alias.c

tests/pdg/inter_alias2.c

tests/pdg/loops.c

tests/pdg/multiple_calls.c

tests/pdg/no_body.c

tests/pdg/pb_infinite_loop.c